Sync Sphinx requirement

1. Sync sphinx dependency with global requirements. It caps python 2 since
sphinx 2.0 no longer supports Python 2.7.
2. Update some URLs to latest
3. Update the UPPER_CONSTRAINTS_FILE for tox[1]

[1]: http://lists.openstack.org/pipermail/openstack-discuss/2019-May/006478.html

Change-Id: Ief1980f0ff6c13ff0370b22267f2ef9baaa1ab64

README.rst

@@ -149,6 +149,5 @@ There are multiple test targets that can be run to validate the code.
 
 * tox -e pep8 - style guidelines enforcement
 * tox -e py27 - traditional unit testing with python 2.7
-* tox -e py35 - traditional unit testing with python 3.5
 * tox -e py36 - traditional unit testing with python 3.6
 * tox -e py37 - traditional unit testing with python 3.7

doc/requirements.txt

@@ -1,5 +1,7 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
+
 openstackdocstheme>=1.18.1 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD

doc/source/man/openstack.rst

@@ -4,4 +4,4 @@ openstack
 
 Please refer to OpenStack command-line interface `OpenStackClient`_.
 
-.. _OpenStackClient: http://docs.openstack.org/cli-reference/openstack.html
+.. _OpenStackClient: https://docs.openstack.org/python-openstackclient/latest/

tox.ini

@@ -7,7 +7,7 @@ skipsdist = True
 usedevelop = True
 install_command = pip install {opts} {packages}
 deps =
-       -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
+       -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands =
@@ -18,7 +18,7 @@ whitelist_externals = find
 [testenv:pypy]
 basepython = python3
 deps =
-       -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
+       -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
  setuptools<3.2
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt